Topline
Forecasters warn more severe storms in northern California could trigger excessive flooding and landslides this weekend as another heavy band of rain called an “atmospheric river” is expected to hammer the state, after multiple rounds of storms caused widespread floods, heavy damage and killed at least 19 people.
A series of storms called atmospheric rivers have hammered California in recent weeks, and more is … [+]
Key Facts
A series of atmospheric rivers have brought as much as two feet of rainfall in some areas of California, killing more people than the past two years of California wildfires combined.
Scientists believe the atmospheric rivers over the Pacific Ocean have been “stuck” on a storm track without a La Niña climate pattern to disrupt the current path, bringing them straight to California, which had been in the midst of a historic drought, the Scientific American reported.
Atmospheric rivers can carry tremendous amounts of water vapor equivalent to the average amount of water flowing at the mouth of the Mississippi River and dump them in large volumes, according to the National Oceanic and Atmospheric Administration.
They’re most common in California, which records between 30% and 50% of its annual precipitation over “just a few” atmospheric river events.
The so-called rivers, which can be up to 375 miles wide, on average, originate in the tropics, with roughly four or five active ones at any given time, according to the Department of Energy.
In the northern hemisphere, they typically form over the ocean and move eastward, affecting areas like California and the Pacific Northwest, as well as Spain, Portugal and France.
Key Background
California has been facing a round of severe storms starting late last month, when an atmospheric river paired with a sudden drop in air pressure called a “bomb cyclone” brought massive amounts of rain, including 5.46 inches in San Francisco on New Year’s Eve—its second wettest day on record, according to the NWS. Another atmospheric river in northern California earlier this month killed two people and caused two piers to collapse, leaving more than 180,000 homes and businesses without power. Then, a storm in California brought as much as 16 inches of rain to some areas, causing widespread flooding and sinkholes, and prompting officials to make evacuation orders, including one in the wealthy coastal city of Montecito. More than 15,000 California homes and businesses are without power Friday morning as a new band of rain makes its way through the state, according to poweroutage.us (nearly 200,000 lost power during an earlier atmospheric river last week).
What To Watch For
Forecasters at the National Weather Service expect the total rainfall from the new atmospheric river to be lighter in the majority of California than the ones that hammered the state over the past two weeks, although forecasters warn some areas in northern California and southern Oregon could see rainfall rates as high as half an inch per hour. The NWS also warns excessive rainfall could likely cause more flooding, while AccuWeather meteorologists warn it could “renew the risks” of flooding and landslides. Coastal communities in northern California, between the cities of Eureka and Point Arena, are under high surf advisories from the National Weather Service, while inland areas face flood watches, including San Francisco, Santa Cruz and Fresno, California.
Further Reading
Watch: Intense Calif. Flooding Caught On Video, Including One From Ellen DeGeneres (Forbes)
Watch: Storm Batters Northern California—Piers Collapse Amid Widespread Flooding (Forbes)
Source: https://www.forbes.com/sites/brianbushard/2023/01/13/what-is-an-atmospheric-river-heres-why-california-is-getting-hammered-with-them/